A boiler is a vessel in which water is vaporized into steam by the application of heat, typically on a continuous basis. The steam generated is most often used either as a direct or indirect heat transfer medium and/or to generate electric power. High pressure and/or high capacity boilers generally are water-tube boilers in which water is circulated within tubes and the applied heat (combustion products such as flame and hot combustion gases) flows across the outside of the tubes. Some of these water tubes may comprise the walls of the furnace in which the heat-generating combustion occurs.
Most water tubes are in the boiler furnace and therefore leakage in a boiler system can be a very grave matter. For instance, the serious risk of smelt/water explosions caused by leakage in recovery boilers is well recognized in the pulp and paper industry, and industry-wide efforts seeking ways to reduce the risk are on-going. Such goal is of significant interest to recovery boiler manufacturers, insurers and pulp mills which operate recovery boilers which burn organic liquors having high caustic levels. Explosions caused by leakage is not a concern for power boilers which burn oil or natural gas, because leaking water will just flash to steam, but nonetheless leakage decreases boiler operation efficiency and increases boiler maintenance costs, and thus leak detection is desirable. A primary leakage concern for boilers in the chemical process industry is contamination of process streams, for instance in ammonia production plants having an ammonia stream on one side of the boiler wall. The nuclear power generation industry has a serious need to avoid boiler-water leakage because fluids with a high radioactive contamination level are under high pressure and a leakage could spread such contamination outside of the initial containment.
Many technologies have been and are currently being developed for detecting boiler water leaks, particularly furnace-water-wall leaks, at the earliest possible moment. These technologies include the use of steam drum level control, computer algorithm, and others. Among the recently developed technologies for early leak detection is the use of sodium ion concentration to detect tube leaks (balancing the sodium ion mass between the boiler feedwater and blowdown), but the sensitivity of the sodium-specific electrode is affected by pH among other feedwater variables. Some boiler operators are currently using complex computer systems in attempts to use boiler operating data for leakage detection with intricate calculations.
A leak detection method of greater sensitivity is needed, because the early detection of leaks requires detection of an extremely small water loss from a dynamic water system. A leak detection method of great sensitivity must be independent of chemical species that might be present in boiler feedwater in amounts varying with the operation efficiency of the demineralizer, mixed bed polisher or other techniques used to purify the feedwater prior to introduction into the boiler.
It is an object of the present invention to provide a boiler-tube leak detection method of great sensitivity that is both cost efficient and relatively simple to operate. It is an object of the present invention to provide a method for the early detection of leaks which can detect an extremely small water loss from a dynamic boiler water system. It is an object of the present invention to provide a leak detection method of great sensitivity that is independent of quality variations in boiler feedwater, and thus is independent of the operational efficiency of the demineralizer, mixed bed polisher or other techniques used to purify the feedwater prior to introduction into the boiler. These and other objects of the present invention are described further below.